little prop help

[Deano]

My 28 partycat is getting repowered right now with a 600SC. The engine that came out, 7.4 merc, had 385hp. The boat has a bravo III with 24 pitch props on it. Im looking at a couple of used props and I am stuck between a 28p and 30p props. I know that the 30 (cupped) is a big jump, but the boat only ran about 55mph with the 7.4 and the hull is just starting to perform at that speed.
what to do? go with the 28p and have them redone if not enough or 30p and hope the damn thing will even get on a plane?

[DMOORE]

Deano,
The 30p is a really big jump from what you have now. It is also going to put a lot more stress on your outdrive. Being a deck, I'm sure there are times that have got a bunch of people on it. As you stated ,it might make it a bit hard to get on plane with the 30p. I think that the 28p would be a better suit to a deck with the bIII. The 28p will still give you a really big improvement.
Darrell.

[DMOORE]

BTW, who it the manufacturer of your boat?
Darrell.

[It's Only Money]

28p

[Deano]

Advantage 28'r. I wired the guy 450.00 for the props (30p) about an hour ago.
The props are new and a good deal. I'll run em for the weekend and see what happens. I might bring them into hill and have them reworked if needed.
The boat has tabs on it that will help alot. Ill let you guys know what happens. Thanks for the input.

[DMOORE]

DEANO,
I'm actually running the same hull design. I have a 28ft Advantage Sport Cat.
I'm running twin motors so unfortunatly the set up is apples to oranges. Sorry I couldn't help more on yours. For what it is worth, I'm changing back to larger props for my boat. I called Advantage and spoke with Bob Wilsey. Thier techinical guru and customer service guy. What a gentleman. VERY VERY friendly and helpfull. It might be worth a call. The good news is if the 30's don't work out for you, they can always be re-pitched. Good luck, hopefully they will work-ouy for you. Keep us posted.
Darrell.

[Deano]

yea, Its going to be a trial and error thing. There are alot of variables that need to be considered. the other props would have me bouncing off the rev limiter (5K) with two people and gas. I couldnt even get it to 5k with 10 people, coolers, etc..
Looking/reading about similar set ups leads me to believe that I can get low 70s. For the boat to be over 70mph (according to prop calcs at .15 slip) 5,200 rpm limit, I need a cupped 30p.
I am also installing a intercooler after this season so Ill pick up a few more ponies. :)
Ill let you know how it goes...

[DMOORE]

Just to let ya know. The motors in my boat started out as 600SC's. Bob Wilsey told me that after adding the Supperchillers and pullies only, they dyno'd out at 750hp!!! Pretty big gain. They have since been taken up to 800's with cams and such.

[ELIMINAT THIS]

Just to let ya know. The motors in my boat started out as 600SC's. Bob Wilsey told me that after adding the Supperchillers and pullies only, they dyno'd out at 750hp!!! Pretty big gain. They have since been taken up to 800's with cams and such.
Nice,so how does your 28' sport cat run with 2 800's.... :)

[DMOORE]

Nice,so how does your 28' sport cat run with 2 800's.... :)
Well, the boats still pretty new to me. Still getting use to it. Also it is under proped right now, running 30p Bravos. I've seen 110 on it with 100 gallons fuel and 2 people, and it still had more to go. Ran out of river, (or mabey balls). Bob Wilsey at Advantage, who set the boat up says he has been over 130 with 32p Bravos. I am going to reprop, up to 32 or 34p Bravos .I think it has more than enough hp for 34's with the boats weight. May decrease cruise rpm nicely. Have to see. I wish it was less trial and error for prop selection.
Darrell.

[Deano]

I wish it was less trial and error for prop selection.
yea, no kidding. I went out and ran the 30s over the weekend. The engine would only hit 4300 rpm. I put my 24s back on and cruised around for the rest of the weekend.
I just dropped them off at Bronson/hill to get labbed and repitched. I am going down to a 28 and see what happens. I think I still made the right choice being that the 28s I was looking at were about $ 150.00 more and would need to get reworked anyways, due to the inefficiency of the bravo III out of the box.
It looks like I am running way too rich also. So I am gambling with the props again until I rejet.
Ill let you guys know how it works out next weekend.

[Party Cat]

What ratio is your drive ???
I was told by Mercruiser that the Bravo III's top out at around 60-65 mph....at that speed they tend to blow out....At the LA Boat Show last year (2005), They told me of a new prop setup that should be out by now....it's a 3 blade front and a 4 blade rear....it's supposed to not blow out at those speeds.....

[Deano]

It has a 1.8 ratio
I talked to Byron Bronson about the new props and he agrees that the four blade will have to much stern lift and I definitely don't need that. The boats attitude is close to your 26, as in front heavy. Hopefully he can work his magic and make the three blades work.
There are a few guys over on OSO running high 70s with the same setup, but the boats are smaller. Hopefully the hull performs better (packs more air) and the props can hang.

[Partycattin]

A friend has a 28' Partycat with a 502(some mild upgrades)and Bravo 3 drive. He recently went 30's and has been happy. The boat is always full of people and still seems to get out of the water pretty well.

[Deano]

does he have a 1.8? If so, my engine is lacking power. It is supposed to have
600hp

[Party Cat]

My 26 has a 600+hp 509 with a 2.0 Bravo III....
With standard 28's I got around 55 mph out of it....My setup also has a 2" spacer putting the props lower than they probably should be...
I had Kevin at R&R Prop Shop in Vegas cup the props and I was able to get a 62.5 gps....
I know my boat is on the heavy side...(~7500lbs on the trailer)
If your HP is correct...then I would think that you should be close on the 28's...I have no problems spinning the motor to 5500 rpms....I thought of going to 30's...but the stress on the drive wasn't worth the few extra mph that it might bring....

[Party Cat]

IHopefully he can work his magic and make the three blades work.
I had the same decision to make...it cost me $300 to have my 28's cupped vs over $1k for the new Merc props that probably wouldn't do much better than modified 28's......

[Deano]

thanks for the info. I hope the 28s work out. I am rejetting this week and running the new props this weekend.
with your calcs and actual prop slip (17%) I will be just touching 70. Im not sure how our hulls differ, other than 2', so Ill post the results.

[Deano]

I had the same decision to make...it cost me $300 to have my 28's cupped vs over $1k for the new Merc props that probably wouldn't do much better than modified 28's......
If your still interested in the new four blade, there is a guy selling a new set on OSO for 650 in the classifieds. Thats who I bought the 30s from. They are only 27s but they are cupped so closer to 28s.

[Party Cat]

thanks for the info. I hope the 28s work out. I am rejetting this week and running the new props this weekend.
with your calcs and actual prop slip (17%) I will be just touching 70. Im not sure how our hulls differ, other than 2', so Ill post the results.
If for whatever reason...ya still can't get the rpms up....I have a clean set of 26's that I won't be using ;)

[Deano]

If for whatever reason...ya still can't get the rpms up....I have a clean set of 26's that I won't be using ;)
nothing like spending a stack and a half of high society to gain a couple mph :p
Maybe Ill trade ya for a nice hill prop, used once :D

[Party Cat]

nothing like spending a stack and a half of high society to gain a couple mph :p
Maybe Ill trade ya for a nice hill prop, used once :D
Too bad ya already had your 30 re-worked....ya could have tried my 28's to see if they would have worked.... :cry: